Why Do you Want Custom Mapping?
All modern engines
are controlled by an electronic brain called the Engine Control Unit (ECU). The files written into this (called the Map) tell your engine how to behave.
Because of the diverse market vehicles are sold in, the settings in this Map must cover all types of conditions for example poor fuel, extremes of temperature or altitude, poor servicing etc. This means of course that as your engine has such generic files written into it, that it is running at less than its full efficiency.